This invention relates, in general, to mechanical switches, and more specifically, to stand-alone hermetically sealed switches.
Most mechanical multi-position switches requiring protection from the environment are constructed using "O" rings made of rubber or some sort of synthetic material similar to rubber. The "O" ring is secured about a shaft or other type of actuator extending into a contact chamber. The chamber is generally completely sealed except where the shaft passes through the "O" ring. The "O" ring is secured tightly about the shaft and does not allow the elements into the chamber. However, over long periods of time, the "O" ring cannot keep water vapor out of the chamber. Water vapor permeates the "O" ring and eventually corrodes the contacts within the chamber. Therefore, switches utilizing "O" rings can only be protected from the open air and environmental conditions for short periods of time without additional protective housing.
There are many applications which require mechanical switches to remain operational over long periods of time. One such application is in the military arena. Munitions, such as free-fall bombs, often require mechanical switches. These munitions are stored for many years at a time before ever being used. The mechanical switches associated with these munitions must be stored in separate hermetically sealed containers to ensure the contacts of the switches are not corroded prior to use. When the munition is to be used, an operator must remove the switch from the container and connect the switch to the munition. Obviously, a hermetically sealed switch which can be stored attached to the munition, therefore eliminating costly packaging, is preferred.
Conventional hermetically sealed switches are push button type switches, and therefore, only one contact or setting can be activated with a single switch. As additional settings are needed, additional push button switches are added. A switch requiring up to 10 settings could be as large as four to five inches across. These types of switches are not practical with munitions or other applications where the associated host device is small.